***AntiGravity Propulsion***
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*** SuperStrings ***
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One sometimes finds what one is not looking for!
- Sir Alexander Fleming -
***Web-Site Up-Dated April, 2003***
The Top 10
Physics Puzzles - Likely a Nobel Prize for each!
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*** SuperStrings - Introduction ***
Superstring theory resolves the most enigmatic problem of twentieth century theoretical
physics: the mathematical incompatibility of the foundational pillars of quantum mechanics
and the General Theory of Relativity. In doing so, string theory modifies our understanding
of spacetime and the gravitational force. One recently discovered consequence of
this modification is that spacetime can undergo remarkable rearrangements
of its basic structure requiring the fabric of spacetime to tear apart
and subsequently reconnect.
Such processes are at best unlikely and probably impossible in pre-string theories
as they would be accompanied by violent physical effects.
In string theory, on the contrary, these processes are physically sensible and
thoroughly common.
The usual domains of general relativity and quantum mechanics are quite different.
General relativity describes the force of gravity and hence is usually applied to the
largest and most massive structures including stars, galaxies, black holes and even,
in cosmology, the universe itself.
Quantum mechanics is most relevant in describing the smallest structures in
the universe such as electrons and quarks. In most ordinary physical situations,
therefore, either general relativity or quantum mechanics is required for a
theoretical understanding, but not both.
There are, however, extreme physical circumstances which require both of these
fundamental theories for a proper theoretical treatment.
String theory is a science in progress; we are still learning new and unexpected things
about it everyday. Whether or not string theory actually describes the universe
that we live in is not known - yet. As we will see it has remarkable potential
to do so.
Think of a guitar string that has been tuned by stretching the string under
tension across the guitar. Depending on how the string is plucked and how much
tension is in the string, different musical notes will be created by the string.
These musical notes could be said to be excitation modes of that guitar string under
tension.
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There are two basic types of string theories:
those with closed string loops that break into open strings,
and those with closed string loops that don't break into open strings.
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In a similar manner, in string theory, the elementary particles we observe in
particle accelerators could be thought of as the "musical notes" or excitation
modes of elementary strings.
In string theory, as in guitar playing, the string must be stretched under tension
in order to become excited. However, the strings in string theory are floating in
spacetime, they aren't tied down to a guitar. Nonetheless, they have tension. The
string tension in string theory is denoted by the quantity 1/(2 pi a'), where a' is
pronounced "alpha prime"and is equal to the square of the string length scale.
If string theory is to be a theory of quantum gravity, then the average size of a
string should be somewhere near the length scale of quantum gravity, called the
Planck length, which is about 10-33 centimeters,
or about a millionth of a billionth
of a billionth of a billionth of a centimeter. Unfortunately, this means that strings are
way too small to see by current or expected particle physics technology (or
financing!!) and so string theorists must devise more clever methods to test the
theory than just looking for little strings in particle experiments.
String theories are classified according to whether or not the strings are
required to be closed loops, and whether or not the particle spectrum includes
fermions. In order to include fermions in string theory, there must be a special kind
of symmetry called supersymmetry, which means for every boson (particle that
transmits a force) there is a corresponding fermion (particle that makes up matter).
So supersymmetry relates the particles that transmit forces to the particles that
make up matter.
Supersymmetric partners to to currently known particles have not been
observed in particle experiments, but theorists believe this is because
supersymmetric particles are too massive to be detected at current accelerators.
Particle accelerators could be on the verge of finding evidence for high energy
supersymmetry in the next decade. Evidence for supersymmetry at high energy
would be compelling evidence that string theory was a good mathematical model
for Nature at the smallest distance scales.
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Excellent sites relating
to SuperString Theory -
UC Santa Barbara Physics Dept. - SuperStrings Web Site - Top-Notch
online tutorial on SuperStrings and Excellent Links
The Official String
Theory Website, An excellent web site about string theory with Biographies on
some of the String Researchers
'Superstring Theory' by Brian Greene,- Cornell University
'String Theory'
by Robbert Dijkgraaf,- University of Amsterdam
A World of
Strings,- from www.HyperMind.com
Stephen
Hawking's Universe,- Web site based on the PBS series - has some info on strings
Michio Kaku - Co-Founder of SuperString Field Theory
Michio Kaku's article on latest SuperString Theory
String theory
in a nutshell,- has a small collection of essays on String Theory
Superstrings and Fundamental theory,-
Part of a larger and Excellent Physics web site from
the Cambridge Relativity Group
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